Low alloy steel containing boron and titanium for high-temperature use



Patented July 6, 1954 LOW 'ALLO' STEEL CONTAINENG HURON- AND EIClAllHJML FOR HIGH- TEMPERATURE USE ClaudeL. Clark, Canton, Ohio", a'ssignor to The Tiniken Roller Bearing Company, Canton, Ohio; a. corporation-of Ohio No Drawing. Application August 28, 1952, Serial No. 306,959

(Cl. H -126) Thisinvention relates to. steels that combine desirable properties at normal temperatures-with excellent high temperature properties. I

Certain parts of. jet engine and gas turbines,v such as their rotors, parts. of aircraft super.- chargers, and. related devices operate at high. stress and elevated temperatures. Various. steels have been developed for such purposes, for instance the well-known. steel alloy disclosed in. United States Patent, No. 2,398,702. In general, the steels used for such purposes up to'the pres-' ent time have been highly alloyed, and it is characteristic of them that. they are very difficult to fabricate, they require special heat treatments of long. duration and, in some instances, are rather complicated, orbecause being highly alloyed they are a drain on strategic metals.

The present shortage of certain critical metals has created the need for. steels of low alloy content that are adapted to replace the highly alloyed} steels used up to the present time for the foregoing and related purposes. In particular, there is a demandv for steels containing a maxi-- mum of 5 per cent of alloying elements, which possess a 1'000-hour rupture strength at 1100"l5.

of at least 40,000 pounds per square inch (p..s..i.) and which also possess good' ductilityto fracture at 1100 F. Steels meeting this combination of requirements have not been available heretofore.

It is among the objects of the inventiontoprovide low alloy steel articles for high temperature use having a satisfactory combination of. high temperature properties, and particularly a rupture strength at 1000 hours and 1100 F. of 40,000, or more, pounds per square. inch, coupled with. desirable ductility to fracture. under those con.- ditions.

A further object is to provide steel articles in accordance with the foregoing object that likewi'se possess desirable mechanical. properties. at."

normal temperatures.

Still another object is to provide. steel. articles embodying the foregoing objects and whoseproperties are developed by a simple and short heat treatment.

Yet another object is to provide steel' articles in accordance with the foregoing objects containing not over about 5- per cent of alloy content.

The invention is predicated. upon. my discovery that its stated objects are attained with steels containing from about 0.15 150 05 per cent ofca'ricon, from 0.0005 to--.004-per' cent of boron, from about 0.75 to 2.5 per cent of chromium, from about 0.2'to 2.0 per cent ofmanganese, fromlabout 0.25. to 1.0 per cent of molybdenum, from about 0.1 to L percent of silicon, from". about 0.2 to. 110' per cent of vanadium, and titanium from about with impurities and elements in amounts that do. not adversely aiiect the properties that characterizethe steels of this invention. For full development of those properties the steels should contain not over about. 0.04 per cent. each of phos phorus and sulfur.

Within the foregoing limits I now prefer that the steels contain from about 0220110 0.35: per cent of. carbon, from 0.001 to 0.003.- per cent of. boron, fromabout 1 to 2 per cent of chromium, from about. 015 to 1.0 per cent of manganese, from about 0.4 to 0.6: per cent of molybdenum, from about 0.5 to- 1.0 per cent of silicon, from about 0.7 to 0.9=per cent of vanadium, and titanium from- 1 to 4 times the amount of carbon.

Steels of the foregoing composition are readily fabricated by all hot forming operations such, for example, as forging, sheet rolling, and piercing into seamless tubes. Likewise, they can be welded readily.

The best combination of strength and ductility at. both. room temperature and at 1100 F. is

developed by air cooling, or normalizing, followedby tempering to about 302/365- Brinell. This heat. treatment produces a martensitic structure. For. maximum ductility in therupturev test: at 1100 F. sections upto 2 inches the steels are normalized at 1800 F. and. tempered at11200 F. This gives a 1-000-hour rupture. strength. of the order 01. 40,000 p. s. i. If a 1'000-hour rupture strength in excess of 45,000 p. s. i. is

desired, with possibly some sacrifice of duetil-ity, the normalizing temperature should be increased: to 1950 F.,. followed by tempering at 1200 F, For larger section sizes the normalizing temperature can be increased, or an oil quench: from 1800 F. or 1900 F. followed by tempering, Without impairing the room temperature or 1100 F: properties.

The excellent. properties of these steels at elevated' temperatures are characteristically exemplified. by the properties'of a steel inaccordance with the invention. and containing 0.22 per cent of carbon, 0.002 per cent of boron, 1.60 per cent of chromium, 0.57 per cent of manganese, 0.48 per cent of molybdenum, 0.77 per cent of silicon, 0.78 percent of vanadium, and 0.35' per cent of of titanium/ This steel when normalized from 1800 F: and tempered 6 hours at 1200 F. had the following room temperature properties:

Tensile strength p. s. i 150,000 02% Yield strength p. s. i 139,250 Elongation in 2", per ccnt 15.5 Reduction of area -do 5.7.1 Brinell hardness 311 321 Furthermore, considering their low alloy content the steels of this invention possess unusually high rupture strength and ductility to fracture at failure. Thus the foregoing steel when heat treated as described had a rupture strength of 440,000 p. s. i. in 1000 hours at 1100 F., while the ductility at fracture was 21.0 per cent. Surprisingly enough, the ductility is four times that of a steel of essentially the same composition but containing no boron or titanium, the 1000 hour rupture strength at 1100 F. of which was 35,000 p. s. i., and the elongation at rupture'5.0 per cent, when normalized at 1800 F. and tempered at 1200 F.

The same steel when normalized from 1950 F. and tempered 6 hours at 1250 F. gave the following room temperature properties:

Tensile strength p. s. i 152,500 0.2% Yield strength do 137,000 Elongation in 2" per cent 15 Reduction of area do 55 Brinell hardness 302/311 while the 1000-hour rupture strength at 1100 F.

was 48,000 p. s. i. and the elongation at rupture was Thus the rupture strength after 1000 hours at 1100 F. is greater than that had by the milder heat treatment while the ductility is equal to that of a comparable steel without boron and titanium.

Thus the steels of this invention containing exceedingly small amounts of boron and small amounts of titanium are much more useful for Work at 1100 F. than similar steels without boron and titanium. And the range of boron stated is critical for when the boron content exceeds 0.005 per cent the high temperature (1100 F.) strength is impaired, and the hot working properties are likewise affected adversely, so much so that at 0.01 per cent of boron the hot Working temperature must be held below 2000 F. Moreover, when heat treated as described the products possess high tensile strength at room temperature, stress-rupture strength in 1000 hours at 1100 F. of at least 40,000 p. s. i. and elongation at rupture of at least 5 percent and as great as 20 per cent.

The high temperature properties of these steels adapt them to the making of parts that are subjected to high stress at such high temperatures as 1100 F., and obviously they represent a major saving of critical alloying elements in comparison with the presently used alloy steels containing several times as much as alloy content as is present in these steels. The properties of these steels adapt them excellently for other purposes also, such as for aircraft brake discs.

According to the provisions of the patent statutes, I have explained the principle and mode of practicing my invention and have described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. Steel adapted for operation at elevated temperatures up to at least 1100 F. which as normalized from about 1800 F. and tempered at 1200 F. to 311 to 321 Brinell has room temperature tensile strength of about 150,000 pounds per square inch, and has a rupture strength in 1000 hours at 1100 F. of at least about 40,000 pounds per square inch and elongation at rupture of about 21 per cent, and having substantially the following composition: carbon 0.15 to 0.5 per cent, boron 0.0005 to 0.004 per cent, chromium 0.75 to 2.5 per cent, manganese 0.2 to 2 per cent, molybdenum 0.25 to 1 per cent, silicon 0.1 to 1.5 per cent, vanadium 0.2 to 1 per cent, and titanium from 1 to 6 times the amount of carbon, and the remainder iron together with impurities and elements in a total amount that does not impair the stated properties.

2. Steel adapted for operation at elevated temperatures up to at least 1100 F. which as normalized from about 1800 F. and tempered at 1200 F. to 311 to 321 Brinell has room temperature tensile strength of about 150,000 pounds per square inch, and has a rupture strength in 1000 hours at 1100 F. of at least about 40,000 pounds per square inch and elongation at rupture of about 21 per cent, and having substantially the following composition: carbon 0.2 to 0.35 per cent, boron 0.001 to 0.003 per cent, chromium 1.0 to 2.0 per cent, manganese 0.5 to 1 per cent, molybdenum 0.4 to 0.6 per cent, silicon 0.5 to 1.0 per cent, vanadium 0.7 to 0.9 per cent, and titanium from 1 to 4 times the amount of carbon, and the remainder iron together with impurities and elements in a total amount that does not impair the stated properties.

3. A hot worked and heat treated steel article for operation at elevated temperatures up to at least 1100 F., the article having been normalized from about 1800 F. and tempered at about 1200 F. to 311 to 321 Brinell and having room temperature tensile strength of about 150,000 pounds per square inch, a rupture strength in 1000 hours at 1100 F. of at least about 40,000 pounds per square inch and elongation at rupture of about 21 per cent, and having substantially the following composition: carbon 0.15 to 0.5 per cent, boron 0.0005 to 0.004 per cent, chromium 0.75 to 2.5 per cent, manganese 0.2 to 2 per cent, molybdenum 0.25 to 1 per cent, silicon 0.1 to 1.5 per cent, vanadium 0.2 to 1 per cent, and titanium from 1 to 6 times the amount of carbon, and the remainder iron together with impurities and elements in a total amount that does not impair the stated properties.

4. A hot worked and heat treated steel article for operation at elevated temperatures up to at least 1100 F. the article having been normalized from about 1800 F. and tempered at about 1200 F. to 311 to 321 Brinell, and having room temperature tensile strength of about 150,000 pounds per square inch and a rupture strength in 1000 hours at 1100 F. of at least about 40,000 pounds per square inch and elongation at rupture in excess of about 9 per cent, and having substantially the following composition: carbon 0.2 to 0.35 per cent, boron 0.001 to 0.003 per cent, chromium 1.0 to 2.0 per cent, manganese 0.5 to 1 per cent, molybdenum 0.4 to 0.6 per cent, silicon 0.5 to 1.0 per cent, vanadium 0.7 to 0.9 per cent, and titanium from 1 to 4 times the amount of carbon, and the remainder iron together with impurities and elements in a total amount that does not impair the stated properties.

, References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,040,189 Strauss May 12, 1936 2,059,893 Naumann Nov. 3, 1936 2,478,420 Payson Aug. 9, 1949 2,531,720 Baeyertz Nov. 28, 1950 2,572,191 Payson Oct. 23, 1951 2,576,229 Krainer Nov. 27, 1951 

8. A HOT WORKED AND HEAT TREATED STEEL ARTICLE FOR OPERATION AT ELEVATED TEMPERATURES UP TO AT LEAST 1100* F., THE ARTICLE HAVING BEEN NORMALIZED FROM ABOUT 1800* F. AND TEMPERED AT ABOUT 1200* F. TO 311 TO 321 BRINELL AND HAVING ROOM TEMPERATURE TENSILE STRENGTH OF ABOUT 150,000 POUNDS PER SQUARE INCH, A RUPTURE STRENGTH IN 1000 HOURS AT 1100* F. OF AT LEAST ABOUT 40,000 POUNDS PER SQUARE INCH AND ELONGATION AT RUPTURE OF ABOUT 21 PER CENT, AND HAVING SUBSTANTIALLY THE FOLLOWING COMPOSITION: CARBON 0.15 TO 0.5 PER CENT, BORON 0.0005 TO 0.004 PER CENT, CHROMIUM 0.75 TO 2.5 PER CENT, MANGANESE 0.2 TO 2 PER CENT, MOLYBDENUM 0.25 TO 1 PER CENT, SILICON 0.1 TO 1.5 PER CENT, VANADIUM 0.2 TO 1 PER CENT, AND TITANIUM FROM 1 TO 6 TIMES THE AMOUNT OF CARBON, AND THE REMAINDER IRON TOGETHER WITH IMPURITIES AND ELEMENTS IN A TOTAL AMOUNT THAT DOES NOT IMPAIR THE STATED PROPERTIES. 